How to set -Os instead of default -O0?

[fbenamrouche]

Hello,

How can I override the default -O0, when using ambiqsuite-sdk? i suppose this requires a modification of the builder?

Thanks!

[nigelb]

Hi @fbenamrouche,

You can try adding a build_flags to your platformio.ini file:

build_flags=-Os

If the builder needs to be modified I can probably make that happen on the weekend.

Nigel.

[fbenamrouche]

The -O0 is hardcoded in the builder. But I think using build_unflags=-O0 works together with build_flags=-0s

[nigelb]

Hi @fbenamrouche,

Sorry for taking so long to get back to this. I have been looking into this and when I look at GCC's man page I see this:

If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.

And the platformio.ini's build_flags end up after the build flags set by the builder:

arm-none-eabi-gcc -o .pio/build/SparkFun_RedBoard_Artemis/libcc3/wsf/port/freertos/wsf_assert.o -c -mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard -ffunction-sections -fdata-sections -fomit-frame-pointer -MMD -MP -std=c99 -Wall -g -O0 -Werror=return-type -Wall -Os ....

And when I tested this I definitely get a different build size:

With -Os in build_flags:

arm-none-eabi-objcopy -O binary .pio/build/SparkFun_RedBoard_Artemis/program .pio/build/SparkFun_RedBoard_Artemis/firmware.bin
Checking size .pio/build/SparkFun_RedBoard_Artemis/program
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM:   [=         ]  10.8% (used 42568 bytes from 393216 bytes)
Flash: [=         ]  11.4% (used 112228 bytes from 983040 bytes)

Without -Os in build_flags:

Checking size .pio/build/SparkFun_RedBoard_Artemis/program
arm-none-eabi-objcopy -O binary .pio/build/SparkFun_RedBoard_Artemis/program .pio/build/SparkFun_RedBoard_Artemis/firmware.bin
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM:   [=         ]  10.8% (used 42612 bytes from 393216 bytes)
Flash: [==        ]  17.3% (used 170076 bytes from 983040 bytes)

With build_unflags=-O0 and build_flags=-Os:

Linking .pio/build/SparkFun_RedBoard_Artemis/program
Checking size .pio/build/SparkFun_RedBoard_Artemis/program
arm-none-eabi-objcopy -O binary .pio/build/SparkFun_RedBoard_Artemis/program .pio/build/SparkFun_RedBoard_Artemis/firmware.bin
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM:   [=         ]  10.8% (used 42568 bytes from 393216 bytes)
Flash: [=         ]  11.4% (used 112228 bytes from 983040 bytes)

The output file size for the test with just build_flags=-Os and with build_unflags=-O0 is the same at: 42568 bytes

So to me it looks like there is no real issue, what do you think?

[fbenamrouche]

Hi @nigelb

Sorry for the delay. I discovered the unflag option, so indeed it works like that. For for me we can say that it's not a real issue ;)

Thanks